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Stopwatch & Timer

Browser stopwatch with lap analysis and a separate countdown timer. Pause without losing state, save recent stopwatch records locally, and use an optional completion sound.

Use this result well

Inputs that matter
Stopwatch start/pause/reset and lap actions, or a countdown from 0–99 hours plus 0–59 minutes and seconds, with an optional completion sound
Output to expect
Elapsed stopwatch time, individual and cumulative laps, fastest/slowest/average laps, saved local records, or remaining countdown time and progress
How it works
The stopwatch derives elapsed time from performance.now(); the countdown derives remaining time from a target timestamp so delayed callbacks catch up while the page remains active
  • Changing modes pauses but preserves each mode’s current state; resetting a nonzero stopwatch saves at most 20 local records and clearing history requires confirmation.
  • Browser throttling, device sleep, page closure, and audio policies can delay or suppress visible updates or sound, so do not use this as a certified or safety-critical timer.

Choose your path

Built around the job you need to finish

Measure elapsed time and manual laps or run one browser countdown without losing paused state when switching modes.

Workout or practice user

Record repeatable manual splits and compare pacing.

Start the stopwatch, record two or more laps, pause, and inspect individual/cumulative plus fastest/slowest/average values.

Can copy or print a reconciled lap list and understands device/browser latency limits.

Short-task countdown user

Set an exact duration and receive a noncritical completion cue.

Switch to Countdown, enter integer hours/minutes/seconds, choose sound, and start or pause.

Zero duration cannot start, a one-second run ends at 00:00, and the user knows page closure, sleep, or policy can suppress the alert.

Returning session reviewer

Keep selected stopwatch results without account sync.

Reset a nonzero stopwatch to save it locally, review up to 20 records, and explicitly confirm history clearing.

Understands records belong to this browser and destructive clearing does not happen from one accidental click.

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Projects using Stopwatch & Timer

This tool is part of these guided projects. Each project provides step-by-step instructions with checklists and all the tools you need in one place.

Daily Routine Decision Record

Document one person’s real routine, constraints, fatigue signals, access needs, and bounded experiments without turning timers or calculators into health or productivity prescriptions.

6 steps6 toolsStart project

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Reference & details

How it works

Elapsed-Time Clock

Derives elapsed stopwatch time from performance.now() and renders hundredths of a second. The underlying clock is high resolution, but the displayed result remains subject to browser and device latency.

Lap Time Management

Records and displays split times with automatic lap numbering and duration calculation between laps.

Countdown Mode

Computes remaining time from a target timestamp, supports pause/resume, and can play an optional browser-generated tone when the open page observes completion.

Updated: August 2026

Example Scenarios

A coach uses the stopwatch to time athletes' sprints and record lap times for performance analysis.

A science student uses the timer to precisely measure reaction times and duration of chemical processes.

A home cook runs one countdown and keeps a separate safety-rated appliance timer as the authoritative alert when timing is critical.

FAQ

Elapsed time is derived from the browser's high-resolution performance clock and displayed to hundredths of a second. Display refresh, input latency, device sleep, and browser scheduling still limit real-world measurement, so it is not a certified timing instrument.

Yes, press the lap button during timing to record split times. All lap times are displayed in a list and can be compared.

Yes, switch to countdown mode, enter your desired duration, and start. An alert sounds when the countdown reaches zero.

While the page remains open, the countdown recalculates from a target timestamp so it can catch up after delayed background callbacks. Device sleep, page closure, throttling, and audio policy can still delay or suppress the visible update or sound.

You can record and compare manual laps, including fastest, slowest, and average lap duration. It does not schedule repeating work/rest intervals; use the separate countdown one interval at a time or choose a purpose-built interval timer.

About Stopwatch & Timer

Run a high-resolution browser stopwatch with laps or a target-time countdown. Modes preserve paused state, recent stopwatch resets can be saved locally, and the page clearly explains browser, sleep, and alert limits.